The aim of this study is to compare disease-free survival (DFS) and overall survival (S) of high risk primary breast cancer patients with negative axillary lymph nodes treated with standard adjuvant chemotherapy with CMF for six cycles or with chemotherapy using CAF for six cycles. Along with this, the study will assess the value of the addition of tamoxifen for five years compared to no tamoxifen in these patients and compare the relative toxicity of these therapies.